Thermal switch with flexible vane

ABSTRACT

A thermally operable switch including a vane which is movable between a stable position and an unstable position in response to thermal expansion and contraction of a part associated with the vane. Contacts operable in response to said movement of the vane, and lagging associated with said part, the lagging increasing the cooling time of said part, and thereby increasing the time interval between consecutive operations of the contacts.

United States Patent Eric Bernard Parkes Birmingham, England Appl. No. 835,056

lnventor Filed June 20, 1969 Patented June 1, 1971 Assignee Joseph Lucas (Industries) Limited Birmingham, England Priority July 2, 1968 Great Britain 31454/68 THERMAL SWITCH WITH FLEXIBLE VANE 2 Claims, 7 Drawing Figs.

U.S. Cl

Int. Cl Field of Search 337/139, 337/127 ..H0lh 37/50 337/127, 135, 136,138, 139, 140

[56] References Cited UNITED STATES PATENTS 3,244,840 4/1966 Broekhuysen....

2,842,642 7/1958 Colomboetal.. 2,706,228 4/1955 Welsh Primary ExaminerBernard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorneyl-lolman and Stern ABSTRACT: A thermally operable switch including a vane which is movable between a stable position and an unstable position in response to thermal expansion and contraction of a part associated with the vane. Contacts operable in response to said movement of the vane, and lagging associated with said part, the lagging increasing the cooling time of said part, and thereby increasing the time interval between consecutive operations of the contacts.

PATENTEnJuN 1|97| 3582.855 SHEET 2 BF 2 BYDW M ATT6 NEYS THERMAL SWITCH WITH FLEXIBLE VANE This invention relates to thermally operable switches of the kind including a vane which is movable between a stable position and an unstable position in response to thermal expansion and contraction of a part associated with the vane, and contacts operable in response to said movement ofthe vane.

According to the invention in a switch of the kind specified, said part associated with the vane is lagged so that cooling time of the part is increased, thereby increasing the time interval between consecutive operations of said contacts. One example of the invention is illustrated in the accompanying drawings wherein:

FIG. 1 is a side elevational view of a thermally operable switch with part of the switch cover broken away,

FIG. 2 is a plan view of the switch shown in FIG. 1 with the cover removed,

FIG. 3 is an enlargement of part of FIG. 1,

FIGS. 4 and 5 are enlarged sectional views of first and second modifications respectively,

FIG. 6 is an enlarged plan view of a third modification and FIG. 7 is a view similar to FIG. 2 of a further modification. Referring first to FIGS. 1 to 3 of the drawings, the switch includes a generally rectangular spring steel vane 11 which is urged by its own resilience to a stable position, and which is nonnally maintained in an unstable, stressed position by a metal strip 12 secured at its ends to diagonally opposite cornets of the vane 11. The vane 11 is secured at one point, to the fixed base 13 of the switch through a support member 14, so that movement of the vane 11 between its stable and unstable positions causes part of the vane to move bodily relative to the base 13 of the switch. A movable contact 15 is carried by the vane 11, and a fixed contact 16 is carried by the base 13. The switch is a normally open switch, and so the fixed contact 16 is so positioned with respect to the movable contact 15 that the contacts 15, 16 are open when the vane 11 is in its unstable position.

In order to operate the switch the strip 12 must be heated so that it expands, and thereby allows the vane 11 to return to its stable position. For this purpose there is provided a heater winding 17 which is associated with the strip 12. Thus, when the heater winding 17 is energized the strip 12 becomes heated and expands and the vane 11 snaps to its stable position, and similarly when the heater winding 17 is deenergized the strip 12 cools and contracts and thereby moves the vane 11 back to its unstable position.

In order to increase the cooling time of the strip 12, and thereby increase the time during which the contacts 15, 16 are open, the strip is lagged. The lagging can take a number of forms, the preferred form being a plane aluminum strip 18 (FIG. 3) which is held in contact with the operating strip 12 by winding the heater winding 17 around the strip 12 and the strip 18. It will be appreciated, that in addition to increasing the cooling time of the strip, the lagging will also increase the heating up time of the strip.

In the modification shown in FIG. 4, the lagging is constituted by a channel shape aluminum member 19 within which the strip 12 is housed, the walls of the member 19 being peened over at points along the length of the member to trap the strip 12in the member 19 without restricting sliding movement of the strip 12 relative to the member 19. The heater winding 17 is again wound around the lagging and the strip 12, and by varying the thickness and cross-sectional shape of the member 19 the lagging effect of the member 19, on the heating and cooling time of the strip 12, can be altered. Moreover, the heating and cooling time of the strip 12 can be further altered by filling the member 19 with silicone grease. In a modification of the arrangement shown in FIG. 4 the member 19 is of channel shaped cross section only at points along its length.

In the further modification shown in FIG. 5 the lagging is constituted by a flattened aluminum tube 21 which completely surrounds the strip 12, the heater winding being wound around the flattened tube 21.

In the third modification shown in FIG. 6 the lagging is in the form of an aluminum strip 22 consisting of a pair of wide end portions 23 interconnected by an intermediate narrow neck portion 24. The strip 22 is again secured to the operating strip 12 by the heater winding, the heater winding being wound around the strip 22 and the strip 12 throughout the length of the strip 22 so that a portion of the heater winding 17 is in close contact with the strip 12 adjacent the portion 24 of the strip 22. Thus, when the heater winding is energized the operating strip 12 heats up relatively quickly, and the end portions 23 of the strip 22 serve to retain the heat of the operating strip 12 during cooling to provide an increase in cooling time. A similar effect can be produced in the construction shown in FIGS. l, 2 and 3 by extending the heater winding so that it is also wound around part of the strip 12 which is not in contact with the lagging strip 18.

It will be appreciated that materials other than aluminum can be used to form the lagging member 18, 19, 21 and 22, and moreover, the lagging members l8, 19, 21 and 22 can themselves be lagged by binding with asbestos wool or similar material.

The switch is intended for use as a time'delay unit for a windscreen wiper system. The various types of lagging described above can give a wide variation in the operating time of the switch, and so the form of the lagging chosen will depend upon the desired delay between successive operations ,of the windscreen wiper motor.

Although the switch described above is of the normally open type, a normally closed switch can be produced merely by altering the relative positions of the contacts l5, l6, and, moreover, by inserting a further fixed contact engageable by the movable contact in the unstable position of the vane 11, the switch can operate as a changeover switch.

The arrangement described above, wherein the winding 17 extends around the lagging and the strip, and around a portion of the strip which is not engaged by the lagging can, of course, apply to any of the modifications of the switch described above.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A thermally operable switch including:

a vane supported on a base which is movable between a stable position and an unstable position,

a part associated with the vane, thermal expansion and contraction of the part serving to move the vane between said stable position and said unstable position, I

A movable contact carried by said vane, a fixed contact mounted on said base, said contacts operable in response to said movement of the vane,

lagging on said part, the lagging increasing the cooling time of said part, and thereby increasing the time interval between consecutive operations of said contacts, and,

a heater winding associated with said part, said heater winding being wound around the lagged portion of said part, and also around an unlagged portion of said part.

2. A thermally operable switch including:

a vane supported on a base which is movable between a stable position and an unstable position,

a part associated with the vane, thermal expansion and contraction of said part causing movement of said vane between stable position and said unstable position,

a movable contact carried by said vane, a fixed contact mounted on said base, said contacts operable in response to said movement of the vane,

a strip of material in contact with said part, and constituting lagging on said part, so that the cooling time of the part is increased, thereby increasing the time interval between consecutive operations of said contacts, said strip of material including a wide portion and a narrower portion, and,

a heater winding which is wound around the lagged portion of said part, the portion of the heater winding engaging the narrower portion of said strip being in closer proximity to said part than the portion of the winding engaging the wide portion of the strip. 

1. A thermally operable switch including: a vane supported on a base which is movable between a stable position and an unstable position, a part associated with the vane, thermal expansion and contraction of the part serving to move the vane between said stable position and said unstable position, A movable contact carried by said vane, a fixed contact mounted on said base, said contacts operable in response to said movement of the vane, lagging on said part, the lagging increasing the cooling time of said part, and thereby increasing the time interval between consecutive operations of said contacts, and, a heater winding associated with said part, said heateR winding being wound around the lagged portion of said part, and also around an unlagged portion of said part.
 2. A thermally operable switch including: a vane supported on a base which is movable between a stable position and an unstable position, a part associated with the vane, thermal expansion and contraction of said part causing movement of said vane between stable position and said unstable position, a movable contact carried by said vane, a fixed contact mounted on said base, said contacts operable in response to said movement of the vane, a strip of material in contact with said part, and constituting lagging on said part, so that the cooling time of the part is increased, thereby increasing the time interval between consecutive operations of said contacts, said strip of material including a wide portion and a narrower portion, and, a heater winding which is wound around the lagged portion of said part, the portion of the heater winding engaging the narrower portion of said strip being in closer proximity to said part than the portion of the winding engaging the wide portion of the strip. 